There are certain things that I will budget shop for and others that I won't.
Suspension, brakes and engine parts fall into the "I won't" category.
As you say " Hellwig seems to be the industry standard"....
Timbren may make a great product. I wouldn't know.
If there warrantee is as good as Hellwig the only other thing I'd check is customer feedback.
I just checked . The Timbren are a bump stop system ( non adjustable ) and run about $279.95 per set. AT Leaf Springs, Helper Springs and Suspension Parts | SD Truck Springs
The Hellwig Load pro 25 helper springs are $302.75 and are adjustable. At Truck Suspension, Bilstein Shocks, Firestone Air Bags, Timbren, Leaf Springs - TruckSpring.com
I'd spend the extra cash.